1. Technical Field
The present invention relates to a display device, more particularly relates to a cathode-ray tube (CRT) type of display device having a set protecting function for sensing an abnormal voltage generated from a horizontal deflection circuit and a high voltage output circuit and for providing reliable protection of the same circuits based upon the sensed abnormal voltage.
2. Background Art
Generally, a display device such as a CRT type of monitor is a peripheral device which processes information data received from an information data system such as a computer system and provides a visual display of processed information data on a screen. Such a monitor is typically available in either black and white which is known as a monochrome monitor or high resolution color which is known as a color graphics adapter (CGA), video graphics adapter (VGA) and enhanced graphics adapter (EGA) monitor. Monochrome, CGA, and EGA monitors provide a visual display of graphics data by processing digital signals. VGA monitors, by contrast, provide a visual display of graphics data by processing analog signals. In all display devices, the video signal is typically received from a video card installed in an information data system in accordance with vertical and horizontal synchronization signals for a visual display.
A display device can generally include a micro-processor which receives the vertical and horizontal synchronization signals from the video card to control the visual display of information data on a screen, and vertical and horizontal deflection circuits which respectively receive the vertical and horizontal synchronization signals to perform a vertical and horizontal deflection, such that an electron beam generated from an electron gun of a CRT is deflected in a regular sequence from an upper left portion to a lower right portion of the CRT by way of a deflection yoke in order to form an image. Using high voltage technology, a high voltage generating circuit such as disclosed, for example, in U.S. Pat. No. 5,438,245 for High Voltage Generating Circuit issued to Kii et al., is included to stably supply a high voltage to an anode of the CRT for forming an image in response to a flyback pulse generated from the horizontal deflection circuit. A video amplifier then serves to amplify video signals R, G and B transmitted from the video card to approximately 40 Vpp-60 Vpp for providing energy to each picture.
In such a display device, deflection circuits perform either an electrostatic deflection using an electric field or an electromagnetic deflection using a magnetic field. As a result, an image is formed on the CRT type of monitor from the electron beam projected onto a fluorescent surface of the monitor by flowing a toothed waveform of electric current into horizontal and vertical coils using the electromagnetic deflection. An example of such a horizontal deflection circuit is disclosed in U.S. Pat. No. 4,263,615 for Horizontal Drive Circuit For Video Display issued to Steinmetz et al. Generally, the horizontal deflection circuit includes a horizontal oscillating circuit, a horizontal drive circuit and a horizontal deflection output circuit, and operates in conjunction with a high voltage drive circuit serving as a load circuit for generating an output horizontal signal to a deflection yoke connector of the CRT monitor.
When an LC resonance circuit is used as a load circuit in the output terminal of the horizontal deflection circuit, and if the load circuit is cut off, all energy is concentrated on the horizontal deflection output circuit without a discharging loop. As a result, the horizontal deflection output circuit will become unavoidedly destroyed. Moreover, in the event where the deflection yoke connector is deviated or disconnected from the CRT monitor during assembly, or when power is applied to the display device in the situation where the deflection yoke connector is deviated or disconnected from the CRT monitor due to external impact, the horizontal deflection circuit will also be damaged. Further, when the pattern of the high voltage output circuit is disconnected or cracked, the high voltage output circuit will also be destroyed.
One recent technique to protect operation of the horizontal deflection output circuit from such destruction based on our experience is to connect a deflection yoke connector acting as a direct load against the horizontal deflection output circuit to an exterior of a circuit substrate, so that if the deflection yoke connector is loose, power supplied to the input terminal of the horizontal deflection output circuit can be cut off. While this technique provides some reliable protection for the horizontal deflection output circuit, the horizontal deflection output circuit cannot be fully protected when the deflection yoke connector is not fully connected to the CRT monitor, or when the pattern (soldering-mask) on a circuit substrate ranged from the deflection yoke connector to the load circuit at is disconnected. Accordingly, it has been our observation that further improvements may still be contemplated.